1. Field of the Invention
The present invention relates to an illumination optical apparatus, a relay optical system, an exposure apparatus, and a device manufacturing method.
2. Description of the Related Art
A projection exposure apparatus has been hitherto used in manufacturing a fine semiconductor device of, for example, a semiconductor memory or a logic circuit, using photolithography (printing) techniques. The projection exposure apparatus projects a circuit pattern, drawn on a reticle (mask), onto, for example, a wafer by a projection optical system, to transfer the circuit pattern.
The minimum dimension (resolution) that can be transferred by the projection exposure apparatus is proportional to the wavelength of exposure light used in exposure, and is inversely proportional to the numerical aperture (NA) of the projection optical system. Therefore, the demand for finer semiconductor devices in recent years has caused the wavelength of the exposure light to be shortened, so that an excimer laser, such as a KrF excimer laser (having a wavelength of approximately 248 nm) or an ArF excimer laser (having a wavelength of approximately 193 nm), is used as an exposure light source.
The body of an exposure apparatus (such as an illumination optical system or a projection optical system) and a light source device (including an excimer laser as an exposure light source) are both large. (The light source device will hereafter be referred to as “excimer laser light source device.”) Therefore, when the body of the exposure apparatus and the excimer laser light source device are set, they are often disposed apart from each other by a certain distance. Consequently, an illumination optical apparatus including an optical system (hereafter referred to as “relay optical system”) that guides a substantially parallel light beam, supplied from the excimer laser light source device, to an entrance (light-incident position) of the body of the exposure apparatus is required.
The relay optical system is roughly divided into a conjugate light transmitting relay system and a parallel light transmitting relay system. The conjugate light transmitting relay system includes a 1× magnification relay optical system in which a laser emergent surface (output portion) of an excimer laser light source and an entrance of the body of the exposure apparatus are optically disposed substantially conjugately. The parallel light transmitting relay system guides a substantially parallel light beam from the laser emergent surface to the entrance of the body of the exposure apparatus, regardless of the optically substantially conjugate relationship between the laser emergent surface of the excimer laser light source and the entrance of the body of the exposure apparatus. These technologies are discussed in Japanese Patent Laid-Open No. 2005-203760.
However, in the 1× magnification relay optical system, which is a related conjugate light transmitting relay system, when the distance between the laser emergent surface and the entrance of the body of the exposure apparatus changes, the focal length of a lens must be changed by re-designing the 1× magnification relay optical system. Therefore, the design freedom with respect to the layout of the body of the exposure apparatus and the excimer laser light source device (hereafter referred to as “apparatus layout”) is considerably low.
In the parallel light transmitting relay system, since the light beam that is supplied from the excimer laser light source device is spread by a slight divergence angle, the longer the distance for guiding the light beam (guiding distance), the larger the cross-sectional diameter of the light beam that reaches the entrance of the body of the exposure apparatus. Therefore, for an apparatus layout having a long guiding distance, vignetting of a portion of the light beam in the entrance of the body of the exposure apparatus occurs, thereby reducing illumination.
In addition, in the parallel light transmitting relay system, the magnitude of a Helmholtz-Lagrange invariant amount is increased. For example, the following technology is proposed. That is, in the technology, a plurality of diffractive optical elements are switchably disposed in an optical path of an illumination optical system, and a predetermined light intensity distribution (having an annular shape or a quadrupole shape) is formed at a Fourier transformation position of a surface (wafer surface) to be exposed. However, the light intensity distribution causes blurring of an image to occur due to a positional displacement of the image in accordance with the magnitude of an incident angle distribution of a light beam that is incident upon the diffractive optical elements.
Therefore, for forming the predetermined light intensity distribution with high precision, it is desirable to switchably dispose many diffractive optical elements, to make the diameter of the light beam that is incident upon the diffractive optical elements as small as possible within a range in which breakage does not occur, and to reduce the angle of incidence.
However, in the parallel light transmitting relay system, since the diameter of the light beam is enlarged while the light beam is guided up to the entrance of the body of the exposure apparatus, the diffractive optical elements become large, thereby reducing the number of diffractive optical elements that can be switchably disposed. In addition, even if an optical system that reduces the diameter of the light beam is disposed at an upstream side of the diffractive optical elements, compared to the conjugate light transmitting relay system, the angle of incidence of the light beam that is incident upon the diffractive optical elements becomes larger. This makes it considerably difficult to form the predetermined light intensity distribution with high precision at the Fourier transformation position of the surface to be exposed.
Accordingly, the parallel light transmitting relay system uses a large number of elements that restrict the apparatus layout. Therefore, as with the related conjugate light transmitting relay system, the design freedom with respect to the apparatus layout is low.